Is hydrogen sulfide in well water dangerous?

At levels found in private wells, hydrogen sulfide is an aesthetic problem, not a health threat. The EPA has no Maximum Contaminant Level for H2S in drinking water, only a secondary (aesthetic) standard. Humans can detect the smell at concentrations as low as 0.0005 parts per million, which is far below any concentration linked to health effects. Industrial exposure to high airborne concentrations of H2S is genuinely toxic, but that's a different situation entirely from tap water.

Why does only my hot water smell like rotten eggs?

When only the hot water smells, the source is almost always your water heater, not your well. The magnesium anode rod inside most water heaters reacts with sulfate in the water and produces hydrogen sulfide gas. This is a chemical reaction inside the tank, not a contamination issue in your well. Replacing the magnesium anode with an aluminum/zinc anode typically solves it.

Will a water filter remove the rotten egg smell?

It depends on the concentration. Activated carbon filters work well for low levels of hydrogen sulfide. For moderate levels, aeration, which physically strips the gas out of the water, is more effective and doesn't require replacing filter media as often. For high levels or a bacterial source, chlorination followed by carbon filtration is usually the right approach. No single filter type works for all cases, which is why testing and diagnosing the source first matters.

What causes hydrogen sulfide in well water?

Three main sources: sulfate-reducing bacteria living in low-oxygen groundwater, a chemical reaction between sulfate-rich water and iron or organic matter in the aquifer, and geological sources where the well is drilled through sulfur-bearing rock. A certified lab test can measure H2S levels and identify whether bacteria are present, which determines the right treatment approach.

Does boiling water remove hydrogen sulfide?

Boiling will drive off some hydrogen sulfide gas since H2S is volatile, but it's not a practical treatment. You'd need to boil with the pot uncovered and the steam vented outside, and even then you wouldn't remove it fully. Boiling also concentrates any other dissolved minerals in the water. Proper filtration or aeration is a much better solution.

Rotten Egg Smell in Well Water: Causes and How to Fix It

That rotten egg smell coming from your tap is hydrogen sulfide gas. The smell is unmistakable. And while it’s genuinely unpleasant, the first thing to know is that at levels found in private wells, it’s an aesthetic problem. Not a health emergency.

The second thing to know: diagnosing the actual source changes everything about how you fix it.

The Diagnostic Question Most People Skip

Before you buy any equipment, answer this: does the smell come from both hot and cold water, or only from the hot?

This one question narrows the source down immediately.

Only the hot water smells. The culprit is almost certainly your water heater, not your well. Most water heaters have a magnesium anode rod inside the tank. That rod is there to protect the tank lining from corrosion, and it does its job well. But in water with elevated sulfate levels, the magnesium reacts with the sulfate and produces hydrogen sulfide gas inside the tank. The gas then comes out of your hot water taps.

This is a chemical reaction in the heater, not a contamination issue in your groundwater. The fix is straightforward: replace the magnesium anode rod with an aluminum/zinc combination rod, or install a powered (impressed current) anode. Either option stops the reaction. It’s the cheapest and easiest fix on this page.

Both hot and cold water smell. The hydrogen sulfide is coming from your well water itself. That’s a different problem with a different set of solutions.

Three Sources of H2S in Well Water

When the smell is in both hot and cold water, one of three things is causing it.

Sulfate-reducing bacteria. These are naturally occurring bacteria that live in low-oxygen (anaerobic) groundwater. They reduce sulfate compounds in the water to hydrogen sulfide gas as part of their metabolic process. They’re common in wells near swampy or marshy land, and in wells that have organic matter in the casing. They aren’t harmful to drink, but they produce a lot of gas at relatively low concentrations.

Chemical reactions in the aquifer. Water with high sulfate content can react with iron or organic matter in the aquifer and generate H2S without any bacteria involved. This is more common in areas with certain sedimentary rock formations.

Geological sources. Some wells are drilled through rock formations that contain naturally occurring sulfur compounds. The water picks up H2S as it moves through that rock. There’s not much you can do about the geology, but you can treat the water after it comes out of the ground.

Health Effects: The Honest Version

The EPA has no Maximum Contaminant Level for hydrogen sulfide in drinking water. It appears only on the secondary standards list, the list for aesthetic issues like taste, odor, and color.

Humans can smell hydrogen sulfide at concentrations as low as 0.0005 parts per million. That’s not a typo. Your nose is an extraordinarily sensitive detector for this compound. The smell that’s driving you crazy is present at concentrations that have no documented health effects from drinking.

Industrial hydrogen sulfide exposure is a real hazard, but that involves airborne concentrations orders of magnitude higher than anything you’d encounter from a tap. Don’t let that comparison inflate the risk here.

Source: EPA Secondary Drinking Water Standards

How to Confirm the Source

A certified lab test tells you two things: the H2S concentration in your water and whether sulfate-reducing bacteria are present. Both matter for choosing treatment.

Your state health department maintains a list of certified labs. The USGS also publishes lab locator resources by state. Collect the sample according to the lab’s instructions. H2S is volatile and the sample handling matters more than it does for most other contaminants.

If you haven’t tested your well recently, a full water quality panel makes sense at the same time. See our well water testing guide for what to include.

Treatment Options

The right treatment depends on the source and the concentration. There’s no one-size-fits-all answer here.

Anode rod replacement (hot water only). If your diagnosis points to the water heater, swap the magnesium rod for an aluminum/zinc rod. A plumber can do it in under an hour. Cost is usually under $50 for the rod itself.

Activated carbon filtration (low concentrations). Carbon filters adsorb hydrogen sulfide effectively at low levels, generally below 1 ppm. They’re inexpensive and easy to maintain. At higher concentrations, the carbon gets exhausted quickly and becomes impractical.

Aeration (moderate concentrations). Aeration systems inject air into the water, which physically strips dissolved hydrogen sulfide gas out of solution before it reaches your taps. It’s chemical-free, highly effective, and doesn’t require consumable media. Aeration is the preferred approach for moderate H2S when bacteria aren’t the source.

Chlorination plus carbon filtration (high concentrations or bacterial source). When sulfate-reducing bacteria are confirmed, chlorination is the only treatment that kills them. Shock chlorination of the well is a starting point. For ongoing control, a continuous chlorine feed system treats the water as it enters the home, followed by an activated carbon filter to remove the residual chlorine before drinking. This is the most involved solution, but it’s also the most thorough when bacteria are driving the problem.

One More Thing: Check for Iron

Hydrogen sulfide and iron problems often show up together. The same low-oxygen groundwater conditions that favor sulfate-reducing bacteria also favor iron bacteria and dissolved iron. If your water has a reddish-brown staining problem or a metallic taste alongside the sulfur smell, those are separate issues that need separate treatment.

Iron filtration and H2S treatment aren’t always compatible. Some iron filters are damaged by chlorination, for instance. If you have both problems, test for both before buying anything. See our iron in well water page for what to look for.

The Recommendation

Start by diagnosing the source. Hot water only, and your fix is probably a $40 anode rod. Both hot and cold, and you need a water test before spending anything on equipment.

Don’t buy a whole-house filtration system based on the smell alone. A certified lab test runs $30 to $100 depending on what you include. That’s the cheapest thing you can do before committing to a treatment system that may not match the actual problem.

For treatment options and system reviews, visit the treatment hub.